Orionids meteor shower expected to peak on 21 October
To help you learn about the southern night sky, Sydney Observatory provides a written guide and a sky map or chart each month. This month’s guide is presented by Dr Andrew Jacob (pictured, right), Curator of Astronomy at Sydney Observatory.
This month, find out how to find the South Celestial Pole, and where to find stars and constellations including Crux (the Southern Cross) and the Pointer stars, the Large and Small Magellanic Clouds, the bright star Antares at the heart of Scorpius. Andrew also tells us about some good photo opportunities from the 10th and particularly the 26th onwards with Jupiter, Mars, Venus and the Moon in the pre-dawn sky. And of course, there is the Orionids meteor shower to look out for during the nights and pre-dawn during October.
For all this and more read the transcript below.
SEE THE SKY CHART
We provide an embedded sky map (below) and a October 2015 night sky chart (PDF) which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. To view PDF star charts you will need to download and install Adobe Acrobat Reader if it’s not on your computer already.
BUY THE BOOK
Our annual book, ‘The Australasian sky guide’, by Dr Nick Lomb has more information and star maps for months from December until December inclusive, plus information about the Sun, twilight, the Moon and tides, and a host of other fascinating astronomical information. You can purchase it ($16.95) at Sydney Observatory and Powerhouse Museum shops or other good bookshops, or online through Powerhouse Publishing (additional packing/postage costs apply). You can buy the 2015 book now, or wait until November and buy the 2016 edition.
READ THE TRANSCRIPT (after the jump)
Transcript of the October 2015 monthly sky guide audio
Hello, and welcome to the night sky for October. My name is Andrew Jacob, and I’m the Curator of Astronomy at Sydney Observatory. To make the most of this podcast, you should begin by gathering a few items together. Firstly, you will need a star map. You can download one, a free one, from Sydney Observatory’s website in the Monthly Sky Guide section under the Astronomy tab.
The star map will show you what stars and constellations are visible in the night sky for October 2015 and I’ll be referring to that sky map during this discussion.
As well as the star map, a torch with a red LED or one covered with a few layers of red cellophane will be very useful. The red light will allow your eyes to remain dark-adapted during the evening, yet still allow you to read your star map.
Finally, a pair of binoculars or a small telescope can be very handy. They’re not essential to follow this podcast but they will help you see a few fainter objects and others in more detail. Where I mention binoculars during this podcast you could, of course, also use your telescope.
Now that we have our equipment together, we need to know a few directions and also how to measure angles across the sky. You can find the cardinal directions: north, south, east and west from a compass app on your mobile device or just remember, of course, that the Sun rises in the east and sets in the west. If the Sun is setting at your right shoulder, then you must be facing south.
Another useful direction is the zenith. This is the point directly above your head.
To find your way around the night sky, it helps to know how to measure angles across it. If you hold out your hand at arm’s length and stretch out your little finger and thumb, they span an angle across the sky of about 20 degrees. A fist held out at arm’s length makes an angle across the sky of about 10 degrees. I’ll be using these measurements during this podcast. So a hand span at arm’s length is 20 degrees, and a fist, about 10 degrees.
I will start with discussing the interesting visible stars and constellations in the night sky, and at the end of this podcast, I will add the visible planets and interesting events for October.
Let us begin our tour of the night sky by looking towards the south. If you’re facing south and you look slightly to the right of south, almost to the south-west, you should be able to see two bright stars, one above the other. If you’re in a bright, light‑polluted location, such as central Sydney, they may be the only two stars you can see in that direction. Away from the city and other bright lights, they will be the brightest pair of stars you see towards the south-west.
These two bright stars, one above the other, are known as the Pointers, the two famous pointer stars which help us find the Southern Cross. The Southern Cross is the best known constellation in the southern skies.
On your star map, the two Pointers are clearly labeled. The Southern Cross, however, appears as Crux, which is its Latin name. The brighter of the two Pointers is called Alpha Centauri. The other one is called Beta Centauri. Alpha Centauri is the third brightest star in the night sky, and Beta Centauri is the 10th brightest star.
Alpha Centauri is a very interesting star. Although it looks like a single star to your eye, it is, in fact, a group of three stars. Two of them are close together and the third is too faint to see at all. Through a small telescope, two of the stars are visible. Both are very similar in size and colour to our Sun. They’re orbiting about each other. The third star is called Proxima Centauri, and it is the closest star to the Earth, after the Sun.
Proxima Centauri is a red dwarf and is only visible through large telescopes. It is believed to be orbiting the stars. Proxima Centauri is about 4.2 light years away, or approximately 42 million million kilometres from us.
I mentioned light years. Let me explain what a light year is. Light travels incredibly fast, about 300,000 kilometres every second. This means that light can travel approximately seven and a half times around the Earth in just one second.
The distances in our Milky Way galaxy and our Universe are vast beyond imagining. Light from the Sun takes about eight-and-a-half minutes to reach us. The light from the Moon takes about one-and-a-quarter seconds to reach us. The light from Proxima Centauri takes 4.2 years to reach us. So we can say Proxima Centauri is about 4.2 light years away.
This means we that see the star as it was 4.2 years ago. A light year is simply a distance, and one light year is a distance of about 10 million million kilometres.
Now, let’s get back to the night sky. We’ll return to Alpha Centauri. If you draw an imaginary line downwards from Alpha Centauri, through Beta Centauri, and onward, you will reach the Southern Cross. It’s lying on its right‑hand side, but otherwise it looks just as it does on the Australian flag.
The Southern Cross is very useful, as it can help us find the direction of true south. Hold up your arm, and measure the length of the long arm of the cross using two fingers, from the left‑hand star of the cross to the right‑hand star. Now, measure this distance four times to the left of the cross.
The point you end up at is called the South Celestial Pole, the south pole of the sky. It’s the point in the sky about which all the stars are rotating, but there are no bright stars in this area. It’s just an imaginary point in the sky.
Now, if you drop a vertical line from the South Celestial Pole straight down to the horizon, you’ll find the direction of south on the ground. Here is something interesting you can do if you have a camera that allows you to leave the shutter open. If you take a photograph of the sky to the south, including the South Celestial Pole, and leave your camera shutter open for 10 or more minutes, you’ll find beautiful, circular star trails in your photograph.
Now that we can find the South Celestial Pole using the Southern Cross, take your handspan, which is approximately 20 degrees, another two times, or about 40 degrees in the same direction beyond the Celestial Pole position. You should come across a fairly bright star in the south-east of the sky.
This bright star is called Achernar. Achernar is a hot blue‑white star about 144 light years away from us. It represents the end of the River Eridanus in the sky. Eridanus is the sixth largest of the 88 constellations in the night sky, and it’s been associated with the Nile River, among others.
If you’re in a dark location, well away from city lights, you might have noticed, as you were measuring your handspans across the sky to Achernar, two faint, fuzzy, cloud‑like objects. They’re located between the South Celestial Pole and the star Achernar. These two hazy clouds are called the Magellanic Clouds.
They were first seen by Europeans hundreds of years ago, and are named after the explorer, Magellan. One of the Clouds is slightly larger than the other. This Large Magellanic Cloud, which is about 160,000 light years away, is about halfway down to the horizon from Achernar.
The Small Magellanic Cloud, which is about 200,000 light years away, is just above that. Both clouds are small galaxies that are orbiting our Milky Way galaxy. And they’re gradually being torn apart and absorbed into the Milky Way galaxy.
If you have binoculars, take a look at the Small Magellanic Cloud. You are seeing stars whose light has taken 200,000 years to reach you. Just above the Cloud, with your binoculars, you should see a small, fuzzy star-like object.
In fact, this is not a star. It’s a globular cluster, a ball‑shaped group of several hundred thousand very ancient stars. This one is called 47‑Tucanae. It’s about 16,000 light years away, barely a tenth of the way towards the Small Magellanic Cloud, but it’s still far beyond our solar system.
Let’s turn to the west now. If you’re facing due west, hold out your arm and measure two handspans, or 40 degrees, above the western horizon. You should reach a bright, orange‑coloured star, perhaps twinkling away due to the effects of Earth’s atmosphere. If you’re using your star map, hold it up in front of you, rotate it so that the horizon labeled west is at the bottom. This will orient the map to match the western sky in front of you.
Now, I remember having great trouble seeing colours in stars when I first began looking at the sky. So if you don’t see the orange colour tonight, don’t worry.
This star is called Antares which means the ‘rival of Mars’ because of its orangeish reddish colour. It’s an enormous, red supergiant star, around 400 times the diameter of our own Sun. If you placed it where our Sun is, it would reach out through the solar system and engulf the Earth. It’s a star coming to the end of its life.
Antares is about 604 light years away from the Earth. As a supergiant, it will eventually die as a supernova. However, it’s so far away that this will have no effect on the Earth, although it will be a spectacularly bright sight. Unfortunately, that’s probably going to happen long after any of our lifetimes.
Antares is the heart of Scorpius, the scorpion in the sky, one of the few constellations that really looks like its name. If you have your star map with you, hold it up towards the west with the west horizon at the bottom, as I described earlier, and locate the star Antares on your star map. Just below Antares, you’ll see a short arc of stars which represent the head and shoulders of the scorpion.
Look back up through Antares and above Antares, you should see a large back-to-front question mark of stars stretching up into the sky above Antares and reaching almost overhead. That’s the tail of the scorpion. At the very end of his tail, you can see his sting quite clearly. Scorpius really does look like a scorpion.
Let’s move on. To the right and above the sting of Scorpius is the constellation Sagittarius. It’s supposed to represent an archer, but I’ve never been able to see an archer when I look at this set of stars. All I can see is a rather triangular teapot. On your star map, Sagittarius is highlighted as the Teapot. Can you see the Teapot pouring tea all over the tail of Scorpius?
Just off the tip of the Teapot is an interesting point in the sky. If you’re away from bright city lights and you’ve been outdoors for more than 15 minutes or so, you might have noticed the Milky Way galaxy stretching overhead. It’s a band of faint, milky light stretching from the Southern Cross over on your left up past the two Pointer stars and then continuing to stretch over through the tail of Scorpius and, finally, off to the northern horizon on your right‑hand side.
The centre of our Milky Way galaxy lies just below the tip of the Teapot not far from Scorpio’s sting. It’s a good thing we’re out here near the edge of the Milky Way galaxy and a long way from its centre. At the centre of our galaxy, 27,000 light years away, lies a very large black hole several million times the mass of our Sun. We’re quite safe from it here, out on the edge of the galaxy.
Let’s turn to the right again and look to the north. Again, if you’re using the star map, turn it so that north is at the bottom. There are a handful of bright stars in the northern sky and some fairly faint constellations. Let’s begin by looking directly north. Just 10 degrees, or one fist width at arm’s length, above the northern horizon, you should see a prominent star, probably twinkling wildly because it’s so close to the horizon.
This is the star Deneb in the constellation of Cygnus the Swan or, as it’s sometimes called, the Northern Cross. We’ll come back to the constellation Cygnus in a moment.
Just less than two handspans, or just less than 40 degrees, to the left of Deneb is another reasonably bright star, again, about a fist width or 10 degrees above the horizon. This second star is Vega, the fifth brightest star in the night sky. It’s in the constellation of Lyra the Harp and lies just 25 light years from us. Quite close compared to most other stars you can see tonight.
These two stars form the base of a triangle. Above them about three handspans, or 60 degrees off the horizon, you’ll find the star Altair, which is in the constellation of Aquila the Eagle. Altair may look slightly yellowish in colour. It’s 17 light years away and is about 10 times brighter than our Sun and it spins on its axis very quickly, about once every 10 hours. By comparison, our Sun only spins once in 25 days.
These three stars don’t look particularly special to us in the Southern Hemisphere. In the Northern Hemisphere, however, they’re known as the Summer Triangle. They’re very high overhead and form a noticeable triangle from the Northern Hemisphere. If you ever travel there, have a look for the Summer Triangle made of the stars Deneb, Vega, and Altair.
Let’s return to Deneb for a moment. Down by the northern horizon, due north, Deneb is a blue white supergiant star over 100 times the diameter of our Sun. It really is a giant of a star. Deneb is about 3,000 light years away from us, but even at that extreme distance, it still appears as a bright star in the night sky. Most of the bright stars in the sky are not even half that distance from us. So this must be one very bright star. If it was the same distance from us as Vega, 25 light years, it would cast shadows at night and be visible during the day. If we placed Deneb where the Sun is, we would have been incinerated by its intense ultraviolet light.
As I said earlier, Deneb is in the constellation of Cygnus the Swan. If you have your star map aligned with the stars to the north, so, with the northern horizon at the bottom, it will help you identify the swan. Its wings stretch down to the left and up to the right and its long neck stretches out and up to the left.
Altair, another one of the Summer Triangle stars, sits just above Cygnus in the constellation of Aquila the Eagle. The eagle also has its wings stretching out to the right and left and its head pointing up and to the left. If you’re at a dark site, you’ll be able to see the Milky Way in this region and you’ll see that these two birds, the swan and the eagle, fly along the Milky Way heading south for the northern winter.
Now we’ve looked at constellations and stars to the south, to the west, and to the north. We could turn to the east, but in October, there aren’t many bright stars nor any truly distinctive constellations in that direction so let’s leave the eastern sky until next month.
What are the special events and highlights for October 2015?
Let me note that all the times I am about to mention are in ‘clock’ time, the time a clock would show, either Eastern Australian Standard Time or Eastern Australian Daylight-saving Time as appropriate. Remember that daylight saving begins on Sunday 4th October at 2am – put your clocks and watches forward one hour.
Let’s start with the Moon phases. We begin with Last Quarter on Monday, 5th October at 8:06am. New Moon falls on Tuesday the 13th at 11:06am. First Quarter is on Wednesday 21st at 7:31am. And finally Full Moon is on Tuesday 27th October at 11:05pm.
What planets are visible in October 2015?
Our evening planet this month is Saturn. It spends the month in the west moving from the constellation Libra into Scorpius in the middle of the month. All the while it remains below the star Antares and close to the stars making up the head and shoulders of the Scorpion. On October 16 the crescent Moon appears just below and to the right of Saturn.
In the morning sky there is much more planetary action. Venus, Mars and Jupiter begin a series of conjunctions and groupings that extend throughout October into November. The Moon also joins in occasionally. All three planets are in Leo for the month, low in the eastern sky before dawn.
We begin on Friday October 9 with a spectacular lunar occultation of Venus. The Moon will move in front of and hide, or occult, Venus. The event begins at 05:32am, as seen from Sydney, during early twilight when Venus disappears behind the bright limb of the Moon. From other locations the timings will be slightly different – check the Observations Blog on Sydney Observatory’s webpages closer to the date. The event ends at 06:53am when Venus reappears this time from behind the dark limb of the Moon. However, the reappearance is after sunrise so this may be difficult to observe. If you are observing with binoculars please take great care to avoid eye damage and NOT look at the Sun!
The next day, on October 10, the crescent Moon appears just above Jupiter with Mars, recognizable by its reddish colour, nearby to the left in a triangular arrangement. Venus shines brightly above and to the left.
By the following weekend, on Sunday October 18, the Moon has departed, but Mars passes less than a Moon-width from Jupiter. Venus remains shining brightly above and to the left.
Another week passes and then, on October 26 & 27, Venus passes Jupiter at a distance of just over two Moon-widths. Mars is just below and to the right. Venus will appear as a semi-circle through binoculars because it is now at its greatest apparent distance from the Sun.
The Venus-Jupiter-Mars & Moon show continues into November but that is another story for our November Podcast.
The Orionids meteor shower is on again in October. They should be visible a few days either side of October 21, with the best conditions likely to be in the dark pre-dawn hours of October 22nd. With the Moon absent from the sky on this morning you may see from 15-20 meteors per hour. Take a comfy camp-chair to a dark site, settle in facing towards Orion (to the north) and enjoy a free celestial fireworks show.
Finally, October 2015 marks an interesting centenary in the history of astronomy. On October 12, 1915, astronomer Robert Innes working in South Africa discovered that Proxima Centauri was the closest night-time star. This star, as I have mentioned, orbits the twin stars of Alpha Centauri although it is not visible to the naked eye. Before moving to South Africa Innes lived for several years in Australia. He arrived in Sydney in 1890, as a 28 year old, to establish a wine & spirit business. He was already an accomplished mathematician and had been appointed a Fellow, no less, of the Royal Astronomical Society at age 17. In Sydney he got acquainted with local astronomers: Henry Chamberlain Russell at Sydney Observatory, John Tebbutt at Windsor and Walter Gale (after whom Gale crater on Mars, where the Curiosity rover is presently roaming, is named). While in Sydney he observed double stars and investigated the orbital motions of planets. He also helped establish the NSW branch of the British Astronomical Association, a group that continues to meet at Sydney Observatory to this day as the Sydney City Skywatchers.
If you have enjoyed this podcast and think you might want to regularly check out what’s in the night sky, why not purchase a copy of Sydney Observatory’s book, ‘Australasian sky guide’. It not only contains detailed monthly sky guides but is jam-packed with astronomical information, including the rise and set times for the Sun, the Moon and planets, information about the tides, and a detailed look at our solar system and upcoming astronomical events. The ‘2015 Australasian sky guide’ will be available from November. Only $16.95 from Sydney Observatory and the Powerhouse Museum shops. Or you can purchase it online for which additional costs apply.
For more astronomical information, check our website and blogs. There, you can also find out about visiting Sydney Observatory to use our telescopes or visit our 3-D space theatre or Sydney Planetarium.
You may also like to explore our FaceBook and Twitter accounts. See Sydney Observatory’s website for links to these.
This has been Andrew Jacob from Sydney Observatory with the podcast for October 2015.